Master Chief Petty Officer of the Navy is selected by the Navy Chief of Staff. The MCPON is the senior enlisted member in the Navy, with a 3-star protocol equivalency. The MCPON represents the entire Navy enlisted force, and speaks on behalf of the enlisted members of the service to Navy and UNSCDF senior leadership.

↑ 1.01.1This insignia can be seen attached to the memorial in the ending cutscene (after the level Halo) in Halo 3. This indicates that John was, very likely, promoted "posthumously" - since no one was aware he was actually alive - to this rank.